........ The do it by turning their body instead of using their grip. As long as they connect the hand well to the body, the body does the work and the hand just needs to transfer the force, not initiate it.......

Well, here's my poll "I agree" answer.

All techniques in aikido should be applied with the whole body, not just the hands/ grip/ muscles etc. You should focus on moving your body in such a way as to unbalance uke before trying to do anything else. If you do this first, techniques will manifest themselves as part of that movement. Depending on which way you move your body depends on which technique will appear.

If you just focus on trying to apply technique, many other things get forgotten, consequently you can get into a "fight" and will often resort to using grip and muscle because that is all you remember.

So in answer to the original question, size does not matter if you move your body. Size does matter if you just focus on technique and are "fighting" with uke to apply it.

A difficult problem is easily solved by asking yourself the question, "Just how would the Lone Ranger handle this?"